In recent years, as LSI (Large-Scale Integrated circuit) progresses toward high integration and high speed, a finer pattern rule is being requested. Under such circumstances, the lithography using a light exposure, which has been currently used as a general technology, is approaching the essential limit of resolution derived from the wavelength of a light source.
As the light source for lithography to be used for formation of a resist pattern, g-beam (436 nm) or i-beam (365 nm) of a mercury lamp, KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc., have been widely used, and a double patterning has been investigated for finer patterning.
The double patterning is a technology that is capable of doubling the resolution of a resist, and further facilitate miniaturization of devices. Accompanying with the progress of miniaturization, a dry etching technology and a hard mask material each having high dimensional accuracy have been required. Also, needs for forming deep holes or grooves by dry etching has been heightened in manufacturing a 3-dimensional NAND memory or a capacitor of DRAM (Dynamic Random-Access Memory), etc. Under such a background, a hard mask excellent in etching resistance has been earnestly required.
On the other hand, to prevent a pattern collapse due to shrinkage of the size of a resist pattern, the thickness of the resist film has been thinned, and as a means to prevent the reduction in dry etching resistance due to the film-thinning, a multi-layer resist process has been used. The multi-layer process generally used in this case is a 3-layer (tri-layer) process in which a hydrocarbon film (hydrocarbon under layer film) is formed at a lower layer, an intermediate film containing silicon (silicon-containing intermediate film) is formed thereon, and a resist film is formed thereon. By providing antireflection effects to both of the silicon-containing intermediate film and the hydrocarbon under layer film, high antireflection effect can be obtained. In the age of a liquid immersion lithography in combination with a high NA (Numerical Aperture) lens, incidence angle of light to a substrate becomes shallow, so that reflection of the substrate is increased, and thus, an antireflection film having a high antireflection effect is required. Accordingly, the tri-layer process using a silicon-containing intermediate film and a hydrocarbon under layer film which have excellent antireflection effect was rapidly spread.
For carrying out the lithography for a fine pattern with a narrow focus margin, it is necessary to flatten the base material. In the case that a hydrocarbon under layer film and a silicon-containing intermediate film are formed by spin coating, there is a merit that the film surface can be flattened by a simple and easy process only of spin coating and baking, by applying a material excellent in embedding characteristics. However, these films formed by spin coating have a problem of insufficient dry etching resistance for double-patterning or digging deep holes or grooves.
Accordingly, a metal series film excellent in dry etching resistance has been investigated, and a hard mask, such as a silicon film and a titanium nitride film, formed by sputtering or CVD (Chemical Vapor Deposition) has been widely used. However, the hard mask formed by sputtering or CVD cannot flatten unevenness of the base material, so that it is necessary to flatten the film surface by grinding with CMP (Chemical-Mechanical Polishing) after film formation. In addition, sputtering and CVD require special devices, which increase the cost.
As the metal series film, a material for forming a metal oxide film by spin coating has been proposed, and a method in which a metal hard mask is formed under a photoresist film, a carbon film is formed thereunder, and a pattern is formed by tri-layer process is known (Non-Patent Document 1). Although the metal oxide film has an advantage to have excellent dry etching resistance compared to the silicon oxide film, it shows high absorbance of ArF light, and causes strong reflection from the metal oxide film. It also causes metal contamination of a spin coater when the metal oxide is applied by a spin coater.
In the case of forming the metal oxide film by spin coating, it is necessary to raise the baking temperature after spin coating to 250° C. or higher. At this time, if a usual hydrocarbon film is applied as an under layer film, it is thermally decomposed. Therefore, a hydrocarbon material having high heat resistance is required for the under layer film. As the material, there may be mentioned a novolac resin of fluorene bisnaphthol, and aldehyde condensates of carbazole or fluorenone (see Patent Documents 1 and 2).
It is also feasible that an under layer film with high heat resistance is formed by spin coating, and a hard mask such as a polysilicon hard mask is formed thereon. The polysilicon is a hard mask with excellent etching resistance. Forming a multi-layer film with 5 layers in total including two layers of antireflection films of a hydrocarbon film and a silicon oxide film formed on the polysilicon hard mask as well as a resist film formed on the antireflection films, it is possible to achieve excellent antireflection effect, to make the silicon oxide film thinner, and to have excellent etching selectivity in processing the substrate. This is excellent multi-layer constitution free from a risk to cause metal contamination, which have been generated in a method of forming a metal oxide film. On the other hand, since the polysilicon film is formed by sputtering at a substrate temperature of 500° C. or higher, this method subject the under layer film formed prior to the polysilicon film to be heated to 500° C. or higher. In heating at 500° C. or higher, there increases a risk of generating out gas from the film even if the under layer film can endure a temperature of 500° C.
In addition, in the tri-layer process, it has been proposed to form a negative pattern by development with an organic solvent. In this case, a margin for subjecting the silicon-containing intermediate film just below the resist to dry etching processing is insufficient since dry etching resistance of the resist film is markedly lowered under the influences both of remaining the film in which the cyclic protective group having etching resistance has been deprotected, and decreasing the film thickness due to the deprotection of the protective group. Thus, it has been investigated to make the silicon-containing intermediate film thin. At present, the film thickness of the silicon-containing intermediate film generally ranges from 30 to 40 nm. This has been determined by the reason that this range enables reflection of a substrate to be minimized, and the balance between the etching rate for transferring the pattern of the resist film and the etching rate for transferring the pattern of the silicon-containing intermediate film to the hydrocarbon film at the lower layer. On the other hand, to deal with insufficiency of dry etching resistance of the resist film, it is necessary to set the thickness of the silicon-containing intermediate film to 10 to 20 nm. However, when the silicon-containing intermediate film is thinned, two problems arise. One is that reflection of the substrate increases, which leads to the reduction in margin of the lithography. The other is that sufficient resistance cannot be secured for processing the hydrocarbon film at the lower layer by dry etching using the pattern of the silicon-containing intermediate film as a mask.
Also, considering the limit of semiconductor miniaturization, an increased capacity without depending on miniaturization is required in memory devices. In a flash memory, it has been investigated to increase the capacity by using a 3-dimensional memory in which memory cells are vertically laminated. In this case, a hole pattern is formed in the film having dozens of layers being laminated, and a gate electrode is embedded therein to form a transistor. In other words, it is required to form a fine hole by development with an organic solvent as mentioned above, and then perform a dry etching using the same to form a deep hole pattern. Accordingly, such processing requires a hard mask that has excellent etching resistance and is capable of transferring a negative pattern having low etching resistance and of deeply processing the laminated film.
As mentioned above, it is desired to develop a multi-layer film that can reduce reflection of the substrate to form a fine pattern and to process a laminated structure, and allows pattern formation with high dimensional accuracy in dry etching.